I suspect FormulaoneFan is correct, and 5 cars will be elliminated at each stage. Bad news for Force India, they stand even less chance of making it into Q2.

Interestingly the rules make no mention of what should happen if only 20 cars are competing.

E33) QUALIFYING PRACTICE33.1 The qualifying practice session will take place on the day before the race from 14.00 to 15.00.The session will be run as follows :a) From 14.00 to 14.20 (Q1) all cars will be permitted on the track and at the end of this period the slowest seven cars will be prohibited from taking any further part in the session.Lap times achieved by the seventeen remaining cars will then be deleted.b) From 14.27 to 14.42 (Q2) the seventeen remaining cars will be permitted on the track and at the end of this period the slowest seven cars will be prohibited from taking any further part in the session.Lap times achieved by the ten remaining cars will then be deleted.c) From 14.50 to 15.00 (Q3) the ten remaining cars will be permitted on the track.The above procedure is based upon a Championship entry of 24 cars. If 22 cars are entered only six cars will be excluded after Q1 and Q2.33) QUALIFYING PRACTICE33.1 The qualifying practice session will take place on the day before the race from 14.00 to 15.00.The session will be run as follows :a) From 14.00 to 14.20 (Q1) all cars will be permitted on the track and at the end of this period the slowest seven cars will be prohibited from taking any further part in the session.Lap times achieved by the seventeen remaining cars will then be deleted.b) From 14.27 to 14.42 (Q2) the seventeen remaining cars will be permitted on the track and at the end of this period the slowest seven cars will be prohibited from taking any further part in the session.Lap times achieved by the ten remaining cars will then be deleted.c) From 14.50 to 15.00 (Q3) the ten remaining cars will be permitted on the track.

The above procedure is based upon a Championship entry of 24 cars. If 22 cars are entered only six cars will be excluded after Q1 and Q2.